Thermally responsive switch

ABSTRACT

A thermally responsive switch comprising a housing including a metal body with a recess therein. A cap of insulating material is secured to the metal body closing the recess. A disc-shaped bimetallic strip is loosely housed in the recess. The fixed contact is carried by a stiff metal bridge which bridges across the recess. The position of the fixed contact is adjustable. Adjustment being made by a tool inserted through an aperture in the cap.

United States Patent [72] Inventor Antonio Moro Milan, Italy [21] Appl.No. 743,157

[22] Filed July 8, 1968 [45] Patented May 25, 1971 [73] Assignee Soc.per Azioni Fratelli Borletti Milan, Italy [54] THERMALLY RESPONSIVESWITCH 12 Claims, 12 Drawing Figs.

[52] US. Cl 337/380, 337/368, 337/374 [51] Int. Cl ..I-I0lh 37/04, HOlh37/28, HOlh 37/54 [50] Field of Search 337/343, 347, 360, 362, 365,368,372, 374, 380, 381, 94, 110, 349, 354, 373, 375

[56] References Cited UNITED STATES PATENTS 3,255,331 6/1966 Ulanet337/374IX) 3,248,503 4/1966 Huber 337/373(X) 3,329,788 7/1967 Moro337/365 3,223,806 12/1965 Moro 337/381(X) 2,863,024 12/1958 Romine...337/372 2,333,291 11/1943 Brannon 337/372 FOREIGN PATENTS 1,342,4939/1963 France 337/365 Primary ExaminerBernard A. Gilheany AssistantExaminer-Dewitt M. Morgan AttorneyYoung and Thompson ABSTRACT: Athermally responsive switch comprising a housing including a metal bodywith a recess therein. A cap of insulating material is secured to themetal body closing the recess. A disc-shaped bimetallic strip is looselyhoused in the recess, The fixed contact is carried by a stiff metalbridge which bridges across the recess. The position of the fixedcontact is adjustable. Adjustment being made by a tool inserted throughan aperture in the cap.

PATENTEU m2 5 I971 A ttorney- PATENTED M2519?! SHEET @UF 2 fig-lInventor fl/vro/v/o Maze %7 77M Attorneys THERMALLY RESPONSIVE SWITCHBACKGROUND OF THE INVENTION 1. Field of the Invention The thermallyresponsive switch according to the invention is particularly designed tobe mounted on the radiators of engines of motor vehicles for the purposeof opening and closing the electric circuit of an electromagneticcoupling which produces the connection and disconnection of the coolingfan for the radiator water, in accordance with the temperature of saidwater.

More precisely, the switch according to the invention is of the typecomprising a bimetallic strip which, when the tem perature increases,snaps out of position, at the temperature value predetermined duringconstruction, in accordance with the conformation and precalibrationimparted to it before being inserted in the body of the switch, while,when the temperature decreases, the bimetallic strip snaps out ofposition at a temperature value predetermined by means of a calibrationeffected from outside the body of the switch when this is fullyassembled.

One of the requirements for this type of switch is that it should havestandardized dimensions, at least as regards the means by which it isfitted to the radiator, so as to be interchangeable with other typesalready in use in motor vehicles for controlling the connection anddisconnection of the radiator cooling fan.

Fitting of these thermally responsive switches is effected by screwingthem into a flange in the wall of the lower tank of the radiator, whichgenerally has a threaded hole with a standard diameter of 20 mm; anythermally responsive switch intended for this type must therefore have athreaded shank of the above-mentioned diameter.

Reference is made here and hereinafter to the standard diameter of 20mm, which, however, should be regarded purely as an example and notcompulsory for the purposes of the application of the principles andconsiderations on which the present invention is based.

2. Description of the Prior Art In switches of this type heretoforeemployed, it is endeavored to arrange the bimetallic strip in a positionas close as possible to the liquid of which the temperature iscontrolled, or substantially on the bottom of the housing, in acylindrical seat formed in the threaded shank; this means, however, thatthe bimetallic strip must be made with a diameter distinctly smallerthan that of the threaded shank, and therefore relatively small, and inthis case the precalibration, within the restricted tolerance limitsrequired, becomes very difficult indeed, unreliable and costly. Thefinal result, therefore, is that instead of these switches there arevery often preferred the types having two separate devices for settingthe switch from outside for the double calibration in the phase ofincreasing temperature and decreasing temperature, respectively, inspite of the greater cost.

SUMMARY OF THE INVENTION It has now been found that keeping the strip inthe close vicinity of the liquid to be subjected to control ispractically speaking unnecessary, particularly when used as abovementioned for controlling the connection and disconnection of the fan;in the thermally responsive switch according to the invention, it isconsequently proposed to carry the bimetallic strip in a seat above thethreaded shank. In this way, it becomes possible to increase thediameter of the seat for the bimetallic strip suitably and, therefore,that of the strip itself, and it is consequently possible to effectpermanent precalibration of the bimetallic strip with ease beforeassembly, while keeping the threaded shank within the required standarddimensions.

According to a preferred, but not Iimitative, embodiment of the presentinvention, the strip is produced with a diameter equal to that of thethreaded shank, so as to provide optimum conditions for the transfer ofthe heat from the shank to the strip itself.

In addition to this characteristic, the switch according to theinvention presents advantageous, but not secondary, improvements whichpermit simple, reliable and cheap construction thereof and which make itpossible to insert it in an electric circuit subjected to higher controlcurrents.

Above the bimetallic strip there is disposed a flexible insulatingtongue which separates it from a flexible conductive tongue insulatedfrom the housing and carrying a first contact in the center; a secondcontact, the fixed position of which can be set from outside the body ofthe switch, is disposed so as to cooperate with the first contact at theinstant when the electric circuit is closed.

The upper part, or cap, of the body of the switch is produced byinjection moulding insulating plastics material and in it 'there areincorporated in the moulding process conductive plates connected to saidfirst and second contacts, respectively; each plate has one endprojecting outside the cap and acts as a pin for effecting connection toa conductor of the electric circuit.

The inner end of a first plate bears directly on a peripheral zone ofsaid conductive tongue carrying the first contact, while the inner endof a second plate bears on a peripheral zone of an insulated metalsupport carrying the second contact. The latter is mounted in thesupport so that it can be set through the medium of screw means adaptedto be actuated from outside by means of a suitable screwdriver passedthrough a hole in the cap; this hole is then closed so that it iswatertight once the operation of setting, or calibrating, said contacthas been carried out.

This setting, in the final calibration stage, is effected so as toposition said second contact with respect to the first contact in suchmanner as to obtain the reverse snap action of the bimetallic strip whenthe falling temperature reaches the predetermined value.

BRIEF DESCRIPTION OF THE DRAWINGS The object of the invention, theconstruction thereof and its operation will appear more clearly,however, from the following description of a number of preferredconstructional forms illustrated in the accompanying drawings, in which:

FIGS. I and 2 are vertical sectional views of the switch in planesdisposed at with respect to one another;

' FIG. 2b shows in section a detail of the insulating tongue and of themovable contact;

FIG. 3 shows the device in plan view;

FIG. 4 illustrates in detail in plan view the flexible tongue carryingthe movable contact;

FIG. 5 is an axial section of the bimetallic strip;

FIG. 6 shows in detail the bridge-shaped support carrying the fixedcontact;

FIG. 7 and 8 show in vertical section two modified constructional formsof the switch according to the invention;

FIG. 9 shows in detail in perspective view of the plate carrying thefixed contact in the constructional form of FIG. 8;

FIGS. I0a and 10b are two axial sections of two modified constructionalforms of the threaded shank of the switch.

DESCRIPTION OF THE PREFERRED EMBODIMENTS A metal housing body 1 has ahollow cylindrical zone 2 with a recess 3 in which is freely housed thebimetallic strip 4 in the form of a bent disc and having, in the case inquestion, its diameter 5 approximately equal to the diameter of thethreaded shank 6.

Obviously, the dimensions of the housing I and the diameter of thebimetallic strip 4 may be different, within certain limits, but ispreferable to keep the diameter of the bimetallic strip substantiallyequal to that of the threaded shank so that the transmission of heatfrom the latter may be as uniform as possible over the entire extent ofthe strip.

In order to make the snap action of the bimetallic strip 4 reliable andclean, the strip is preferably shaped with a diametral section such asappears in FIG. 5, that is with a central portion 4' formed with aslight curvature opposite to the main curvature, or even like a veryopen truncated cone, and with a diameter about one third of the totaldiameter.

Inside the hollow zone 2 and above the bimetallic strip 4 there isdisposed a flat ring 7 with a radial tongue 8 projecting as far as thecentral zone and made of insulating material, for example of thecommonly known Mylar type, which has a high resistance to fracture andto high and low temperatures and is an optimum insulating material.

On the ring 7 there bears the ring 9, which is made of material which isa good conductor and from which a flexible radial tongue 10 projectstoward the center. Towards the end of the tongue, in the center of thering 9 (see FIG. 4), there is provided a hole 11 in which is inserted astud 12 made of metal suitable for electric contacts and having a headwhich is preferably spherical; the stud 12 is fixed with theinterposition of the washer 13 by flanging its tip over in the form of aspherical head 14.

During assembly, a slight clearance is left between said spherical head14 and the center of the bimetallic strip to avoid any possible pressureof said head 14 on the bimetallic strip having an influence on theinstant when the snap action or movement occurs.

On top of the ring 9 there bears another ring 15 of insulating material,on which the bridge-shaped metal support or bridge 16 bears in turn.

The three rings 7, 9, 15 and the bridge 16 are held oriented angularlyand radially by two pins 17 formed in one piece with the cap 18, saidpins being engaged in holes or notches 19, 19'

' prearranged in said parts. The pins 17 are positioned in such mannerthat on assembly the rings 7, 9, 15 cannot be fitted upside-down orturned with respect to the prescribed position.

The four parts 7, 9, 15 and 16 aforesaid are held in position in theseat 2 under pressure from the cap 18 of insulating material, which isheld in the seat in turn by means of the flanged over portion 20 of thehousing 1 with the interposition of the metal ring 2| and the rubberring 22, which ensures watertightness of the interior of the housing 1.

The cap 18 is preferably made by injection moulding suitable plasticsmaterial (for example Dcln'n) and the plates 23 and 24 areincorporatedin said plastics material in the same moulding stage; that part of theplates which extends outside the cap 18 has the function of a pin forconnection to the conductors of the electric circuit.

The contraction of the plastics material (Delrin or the equivalent) bythermal effect produces a strong pressure on the two plates, which aresuitably slotted (see HO. 9), thus ensuring watertightness along thesurface of the plates themselves.

The internal portion of the plate 24 presses by means of its end 25 on aperipheral zone of the bridge 16, thereby producing electricalcontinuity; the internal portion of the plate 23, on the other hand,presses by means of its end 26 on a peripheral zone 27 of the surface ofthe metal ring 9, thereby establishing electrical continuity with thelatter and therefore with the contact 12.

As has been said, when the contact 12 is in the inoperative position itis insulated from all the other metal parts of the device except,obviously, the plate 23.

The bridge 16 is formed centrally in the shape of a bridge (see FIG. 6)in which a threaded hole 28 is provided in a position coinciding withthe axis of the switch; said threaded hole is widened into alongitudinal slot 29, which enables the hole 28 to be pinched andrestricted, due to the flexibility of the two parts separated by theslot, in order to make it possible to produce a certain pressure on thethread of the screw 30 and thus avoid the latter unscrewing as a resultof vibration. The screw 30 carries the electrical contact 31 at itslower end; said electrical contact is therefore electrically connectedto the plate 24 through the metal bridge 16, while it is insulated fromall the other metal parts of the switch.

The fixed contact 31 is coaxial with the movable contact 12 and isspaced therefrom in the inoperative position, as can be seen from thedrawing.

Provided in the cap 18 is a hole 32 through which it is possible toobtain access with a suitable tool, such as a screwdriver, a spanner orthe like, for the purpose of screwing in and unscrewing the screw 30during the stage of calibration of the device for adjusting the reversesnap action of the bimetallic strip 4, that is the snap action at thevalue predetermined for the temperature as it falls, in substantiallyknown manner. In fact, by screwing the screw 30 in, the contact 31 isbrought nearer to the contact 12 and, when the bimetallic strip 4performs its snap action on an increase in the temperature, it isarrested sooner: consequently, the reverse snap action will take placeat a higher temperature. The converse is the case if the distancebetween the two contacts 12 and 31 is increased.

As has already been mentioned earlier, there are no other adjustments tobe carried out, because the snap action, when the temperature increases,takes place at the desired value,

,which is determined solely by the conformation of the bimetallic stripitself, without any other operations. There is thus obtained, in simpleand rapid manner, a switch which is perfectly calibrated at the twotripping temperatures of the bimetallic strip, the increasing anddecreasing-temperature, respectively.

The calibration having been effected through the medium of the screw 30,the threaded hole 32 is closed and sealed by screwing into it aconical-headed screw 33 which is pressed against the flared orcountersunk portion of hole 32.

As a greater safeguard, watertightness may be ensured by covering thehead of the screw with suitable sealing material.

The operation of the switch is obvious: when the threaded shank 6 of thehousing is placed in contact with the water, or other liquid, the heatof the latter is transmitted to said shank and from this to thebimetallic strip 4; when the predetermined temperature value is reachcd,the strip performs its snap action or trips, causing the contact 12 topress against the contact 31. The electric circuit which leads to thetwo plates 23 and 24 is then closed through the end 25, the bridge 16,the contact 31, the contact 12, the disc 9 and the end 26.

When the temperature decreases, the bimetallic strip snaps or trips inthe direction opposite to the previous direction at the predeterminedvalue: the contact 12 moves away from the contact 31 and the electriccircuit is broken again.

The bimetallic strip is constantly maintained at the temperature of theelement with which the device is in contact due to the transfer of heateffected by the metal mass of the threaded shank 6 which, as has beensaid, is always in direct contact with said element; in effect, thetemperature of the latter always varies gradually and notinstantaneously, so that, in prac tice, the mass 6 is never subjected tosubstantial temperature gradients and it can be considered that thebimetallic strip is practically speaking always at the same temperatureas said element.

A modified constructional form is shown in FIG. 7. In this variant, thebridge 16 is dispensed with and its function is performed by the plate24', the internal end 34 of which, bent at right angles at 35, has athreaded hole 28 into which the screw 30 carrying the contact 31 isscrewed directly. All the other elements remain the same as those whichhave already been described in the case of the first constructionalform.

A second modified constructional form is shown in FlG.-8. The bridge 16is also eliminated in this embodiment and is replaced by the plate 24".This plate, in turn, is bent at right angles at 35' and extends in theform of a uniplanar spiral 36, preferably as shown in FIG. 9.

The central terminal end of the spiral 36 is able to undergo smallelastic displacements without being permanently deformed. Fixed to saidend is the contact 31', on the bottom of which the movable contact 12presses on the tripping of the bimetallic strip 4. The adjusting orcalibrating screw 37 bears on the upper face of the contact 31 thisscrew is screwed into the threaded hole 32' provided directly in theinsulating cap 18 and the position of the contact 31' is set by means ofsaid screw in the calibration stage. The calibration having been carriedout, the screw 37 is sealed with a suitable lacquer or cement, so as toensure watertightness and at the same time lock the screw 37 itselfagainst any possible unscrewing due to vibration. I

What has already been described in the case of the first constructionalform applies to all the other elements.

As has been said, in any one of the constructional forms hereinbeforedescribed, the bimetallic strip is constantly kept at the temperature ofthe element with which the device is in contact, due to the transfer ofheat effected by the metal mass of the threaded shank 6, which is alwaysin direct contact with said element; in effect, the temperature of thelatter always varies gradually and not instantaneously, so that, inpractice, the mass 6 is never subjected to substantial temperaturegradients and it can be considered that the bimetallic strip ispractically speaking always at the same temperature as said element.

lt-is possible, however, if certain system conditions make thisadvisable, to modify the threaded shank 6, as shown in FIG. a or FIG.10!). A cylindrical chamber 38 (see FIG. l0a) is formed in the shank 6,leaving a wall 39 of small thickness below the bimetallic strip, and anumber of radial holes 40 are made at the root of the thread to preventthe formation of cushions of air. in an even simpler manner (see FIG.1011), the chamber 38' may be made in the form ofa truncated conewithout any radial holes.

In both these cases, the liquid of which it is desired to control thetemperature is separated from the bimetallic strip by a thickness ofmetal which is reduced to the minimum.

All the constructional forms hereinbefore described may easily bemodified to adapt them to the case where the electric circuit controlledis closed through the mass of the device. To achieve this, the plate 23,26 is eliminated, and thus also the insulating ring 7; the conductivedisc 9 is pressed directly against the body 1 by the cap 18 and theclosing of the circuit is effected through this earthed contact. in thiscase, the bimetallic strip bears directly against the contact 12. Onlythe contact 31 remains insulated and, as before, the contact 12 bearsagainst this at the moment the circuit is closed.

It is understood, however, that the constructional forms hereinbeforedescribed are not to be regarded as restricting the invention, but thatother variants all coming within the scope of said invention may bedifferent therefrom.

Iclaim:

l. A thermally responsive switch having a housing including a metal bodywith a threaded shank for anchorage to a member whose temperature is tocontrol the switch, themetal body having a recess therein, a cap ofinsulating material secured to said body and closing the recess, adisc-shaped bimetallic'strip loosely housed in said recess, a movablecontact and a fixed contact, terminal means connected to said contactsand extending exteriorly of said housing, said strip changing positionat a given temperature to apply the movable contact against the fixedcontact to complete an electric circuit, astiff metal bridge thatbridges across said recess and carries said fixed contact, calibratingmeans accessible from outside the switch to move the fixed contactrelative to the bridge to adjust the temperature at which the contactsmove apart from each other to open said circuit, said body havingshoulders in said recess which support the ends of said bridge, andelectrical insulation means between said bridge and said body.

2. A switch as claimed in claim 1, said cap having an internal cavitythat opens toward said recess, said fixed contact being disposed in saidcavity.

3. A switch as in claim 1, the ends of said bridge on opposite sides ofsaid recess being gripped between said cap and said body.

.4. A switch as in claim I, said bridge having a central portion that isconcave and that opens in the direction of the bottom of said recess.

5. Switch as in claim 1, wherein the central portion of the bimetallicstrip acts on said movable contact through a flexible insulating tongueon said insulation means.

6. Switch as in claim I, wherein said movable contact is fixed to thefree end of a flexible arm projecting radially towards the center from aperipheral ring supported by said shoulders.

7. Switch as in claim 6, wherein a metal plate in said insulating caphas its lower end disposed inside the recess bearing under pressure onsaid peripheral ring carrying the movable contact, so as to establishcontinuity of electrical connection between the contact and the plate.

8. Switch as in claim 5, wherein said metal plate is formed externallyas a pin comprising one of said terminal means.

9. Switch as in claim 5, wherein said insulation means comprises aninsulating ring from which there projects radially a tab forming saidflexible insulating tongue interposed between the movable contact andthe bimetallic strip.

10. Switch as in claim 7, wherein a second metal plate in saidinsulating cap has its lower end disposed inside the chamber bearingunder pressure on a peripheral zone of the surface of said bridgecarrying the fixed contact, so as to establish continuity of electricalconnection between the latter and said plate.

11. Switch as in claim 10, wherein said second plate is formedexternally as a pin comprising one of said terminal means.

12. Switch as in claim l0, wherein the peripheral zone of said bridgecarrying the fixed contact is separated from the ring carrying themovable .contact through the medium of a ring of insulating material.

1. A thermally responsive switch having a housing including a metal bodywith a threaded shank for anchorage to a member whose temperature is tocontrol the switch, the metal body having a recess therein, a cap ofinsulating material secured to said body and closing the recess, adisc-shaped bimetallic strip loosely housed in said recess, a movablecontact and a fixed contact, terminal means connected to said contactsand extending exteriorly of said housing, said strip changing positionat a given temperature to apply the movable contact against the fixedcontact to complete an electric circuit, a stiff metal bridge thatbridges across said recess and carries said fixed contact, calibratingmeans accessible from outside the switch to move the fixed contactrelative to the bridge to adjust the temperature at which the contactsmove apart from each other to open said circuit, said body havingshoulders in said recess which support the ends of said bridge, andelectrical insulation means between said bridge and said body.
 2. Aswitch as claimed in claim 1, said cap having an internal cavity thatopens toward said recess, said fixed contact being disposed in saidcavity.
 3. A switch as in claim 1, the ends of said bridge on oppositesides of said recess being gripped between said cap and said body.
 4. Aswitch as in claim 1, said bridge having a central portion that isconcave and that opens in the direction of the bottom of said recess. 5.Switch as in claim 1, wherein the central portion of the bimetallicstrip acts on said movable contact through a flexible insulating tongueon said insulation means.
 6. Switch as in claim 1, wherein said movablecontact is fixed to the free end of a flexible arm projecting radiallytowards the center from a peripheral ring supported by said shoulders.7. Switch as in claim 6, wherein a metal plate in said insulating caphas its lower end disposed inside the recess bearing under pressure onsaid peripheral ring carrying the movable contact, so as to establishcontinuity of electrical connection between the contact and the plate.8. Switch as in claim 5, wherein said metal plate is formed externallyas a pin comprising one of said terminal means.
 9. Switch as in claim 5,wherein said insulation means comprises an insulating ring from whichthere projects radially a tab forming said flexible insulating tongueinterposed between the movable contact and the bimetallic strip. 10.Switch as in claim 7, wherein a second metal plate in said insulatingcap has its lower end disposed inside the chamber bearing under pressureon a peripheral zone of the surface of said bridge carrying the fixedcontact, so as to establish continuity of electrical connection betweenthe latter and said plate.
 11. Switch as in claim 10, wherein saidsecond plate is formed externally as a pin comprising one of saidterminal means.
 12. Switch as in claim 10, wherein the peripheral zoneof said bridge carrying the fixed contact is separated from the ringcarrying the movable contact through the medium of a ring of insulatingmaterial.